Schizophrenia
Patients with schizophrenia have long been recognized as showing "flat or inappropriate affect, with splitting of feelings from events...feelings seem flat instead of being in contact with what is going on". One study of flat affect in schizophrenia found that "flat affect was more common in men, and was associated with worse current quality of life" as well as having "an adverse effect on course of illness".
The study also reported a "dissociation between reported experience of emotion and its display" – supporting the suggestion made elsewhere that "blunted affect, including flattened facial expressiveness and lack of vocal inflection...often disguises an individual's true feelings': thus feelings may merely be unexpressed, rather than totally lacking. On the other hand, "a lack of emotions which is due not to mere repression but to a real loss of contact with the objective world gives the observer a specific impression of 'queerness'...The remainders of emotions or the substitutes for emotions usually refer to rage and aggressiveness". In the most extreme cases, there is a complete "dissociation from affective states" on the part of the patient: "not only has he hacked his intellect away from his feelings, but he has smashed his feelings and his capacity for judgment into smithereens".
Read more about this topic: Blunted Affect